Apparatus for discriminating sheet material

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Divisional of co-pending U.S. patent application Ser. No. 11/553,069 filed Oct. 26, 2006, currently pending, which is a Divisional of application Ser. No. 10/712,204, filed Nov. 12, 2003, now U.S. Pat. No. 7,182,338, granted Feb. 27, 2007, to which priority under 35 U.S.C. §120 is claimed. The contents of prior applications No. 11/553,069 and No. 10/712,204 are hereby incorporated by reference for all purposes as if fully set forth herein. This application also claims foreign priority benefits under 35 U.S.C. §119 to Japanese Patent Application No. 2002-330273 filed in Japan Nov. 14, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for discriminating the kind of a sheet material.

2. Related Background Art

Recently, sheet-material discriminating apparatuses for discriminating the kind of a sheet material have received attention in various technological fields. For example, it is desirable to automatically detect the kind of paper for use in printers, copiers and other image forming machines for keeping print quality at a satisfactory level. The apparatus for discriminating sheet material will be described below in this respect.

As shown in <figref idref="DRAWINGS">FIG. 11</figref>, a bar <b>106</b> is rotatably supported near a positioning roller <b>103</b> (U.S. Pat. No. 5,962,861). A force F acts on an end <b>105</b> of the bar <b>106</b> in a direction shown by the arrow. Now, the bar <b>106</b> slightly rotates in a clockwise direction (see symbol E) as a printing paper P is fed, but a displacement thereof varies depending on the material of the printing paper. Thus, the kind of the printing paper P can be discriminates by detecting the displacement with a sensor <b>108</b>.

In the conventional apparatus described above, the printing paper P should be deflected under only the influence of the lifting force F from the bar <b>106</b>. However, the printing paper P may be deflected under the influence of wind pressure if the speed at which the printing paper P is fed is high, and the printing paper P may be deflected simply by its own weight if it is thin. Thus, in such a case, it is difficult to discriminate the kind of a paper correctly. In addition, the printing paper P is susceptible to mechanical vibrations.

Thus, the present invention is to provide a new apparatus capable of correctly discriminating the kind of a sheet material. So far as discrimination of a sheet material is concerned, the apparatus and method according to the present invention may be applied without being specifically limited, and also they may be applied even if the speed at which the sheet material is fed is high, and the sheet material is thin.

SUMMARY OF THE INVENTION

The present invention has been made in view of the situations described above, and provides an apparatus for discriminating the kind of a sheet material, comprising:

a substrate having a recessed portion;

a press member situated so as to have access to the recessed portion;

a support member that is deformed as a sheet material situated to cover the recessed portion is pressed by the press member and thereby deflected; and

a sensor for detecting a deformation amount of the support member,

wherein the kind of the sheet material is discriminated on the basis of detecting the deformation amount of the sheet material by the sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

<figref idref="DRAWINGS">FIG. 1</figref> is a schematic view showing one example of a structure (in which a roller <b>2</b> lies outside a groove <b>1</b><i>a</i>) of an apparatus for discriminating a sheet material according to the present invention;

<figref idref="DRAWINGS">FIG. 2</figref> is a schematic view showing one example of a structure (in which the roller <b>2</b> lies in the groove <b>1</b><i>a</i>) of the apparatus for discriminating a sheet material according to the present invention;

<figref idref="DRAWINGS">FIG. 3</figref> is a schematic front view showing another example of a structure (in which a press member <b>12</b> lies outside the groove <b>1</b><i>a</i>) of the apparatus for discriminating a sheet material according to the present invention;

<figref idref="DRAWINGS">FIG. 4</figref> is a schematic side view showing another example (in which the press member <b>12</b> lies outside the groove <b>1</b><i>a</i>) of the apparatus for discriminating a sheet material according to the present invention;

<figref idref="DRAWINGS">FIG. 5</figref> is a schematic front view showing another example of a structure (in which the press member <b>12</b> lies in the groove <b>1</b><i>a</i>) of the apparatus for discriminating a sheet material according to the present invention;

<figref idref="DRAWINGS">FIG. 6</figref> is a side view showing another example of a structure (in which the press member <b>12</b> lies in the groove <b>1</b><i>a</i>) of the apparatus for discriminating a sheet material according to the present invention;

<figref idref="DRAWINGS">FIG. 7</figref> is a schematic front view showing still another example of a structure (in which the roller <b>2</b> lies outside an recessed portion <b>11</b><i>a</i>) of the apparatus for discriminating a sheet material according to the present invention;

<figref idref="DRAWINGS">FIG. 8</figref> is a schematic side view showing still another example of a structure (in which the roller <b>2</b> lies outside the recessed portion <b>11</b><i>a</i>) of the apparatus for discriminating a sheet material according to the present invention;

<figref idref="DRAWINGS">FIG. 9</figref> is a schematic front view showing still another example of a structure (in which the roller <b>2</b> lies in the recessed portion <b>11</b><i>a</i>) of the apparatus for discriminating a sheet material according to the present invention;

<figref idref="DRAWINGS">FIG. 10</figref> is a schematic side view showing still another example of a structure (in which the roller <b>2</b> lies in the recessed portion <b>11</b><i>a</i>) of the apparatus for discriminating a sheet material according to the present invention; and

<figref idref="DRAWINGS">FIG. 11</figref> is a schematic view showing one example of a conventional structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiment of the present invention will be described below with reference to <figref idref="DRAWINGS">FIGS. 1 to 10</figref>.

An apparatus for discriminating a sheet material according to this embodiment comprises a substrate <b>1</b> having a recessed portion <b>1</b><i>a</i>, and a press member <b>2</b> situated to have free access to the recessed portion <b>1</b><i>a</i>, as shown by symbol A<b>1</b> in <figref idref="DRAWINGS">FIG. 1</figref> and <figref idref="DRAWINGS">FIG. 2</figref>. When a sheet material P situated to cover the recessed portion <b>1</b><i>a </i>of the substrate <b>1</b> is pressed with a press member <b>2</b> (see <figref idref="DRAWINGS">FIG. 2</figref>), the sheet material P is pushed into the recessed portion <b>1</b><i>a </i>and thereby deflected, and an elastic support member <b>3</b> is deformed by an amount equivalent to the deflection amount, and the kind of the sheet material P can be discriminated on the basis of detecting the deformation amount of the elastic support member <b>3</b> by the deformation amount sensor S. Amounts detected with the deformation amount sensor S may include:

the deformation amount of the elastic support member <b>3</b> when the sheet material P is most deflected;

both the deformation amount of the elastic support member <b>3</b> when the sheet material P is not deflected and the deformation amount of the elastic support member <b>3</b> when the sheet material P is deflected; and

the ratio of deformation of the elastic support member <b>3</b> in the process of deflection of the sheet material P (i.e. when the change of deformation amount of the elastic support member in the process of change in deflection amount of the sheet material is detected, and the kind of a sheet material is discriminated based on the change in deformation). Furthermore, if the deflection state can be varied depending on whether the sheet material is pressed with the press member or not, it is not required that the recessed portion on the substrate should be completely covered with the sheet material.

The apparatus for discriminating a sheet material according to the present invention has press member holding means <b>4</b> for holding the press member <b>2</b>, and the press member holding means <b>4</b> should

hold the press member <b>2</b> at a distance from the substrate <b>1</b> when the sheet material P is set in the substrate <b>1</b>, and

move the press member <b>2</b> to a position near the recessed portion <b>1</b><i>a </i>when the sheet material P is pressed.

Furthermore, as shown in <figref idref="DRAWINGS">FIGS. 3 to 6</figref>, the press member <b>12</b> held by press member holding means <b>14</b> may be moved by rotating press member holding means <b>14</b>.

In addition, the press member holding means may hold the press member so that the press member contacts the sheet material P at a position other than the recessed portion.

Furthermore, as shown in <figref idref="DRAWINGS">FIG. 1</figref>, a first memory B<b>1</b> for storing as data a relationship between the output signals of the deformation amount sensor S and the kind of the sheet material, and a first discrimination unit C<b>1</b> for discriminating the kind of the sheet material P from the output signals of the deformation amount sensor S and data in the first memory B<b>1</b> may be provided.

On the other hand, if “the deformation amount of the elastic support member <b>3</b> when the sheet material P is not deflected” and “the deformation amount of the elastic support member <b>3</b> when the sheet material P is deflected” are detected as described above, the press member holding means <b>4</b> described above may move the press member <b>2</b> along the sheet material P, and

the sheet material P is not deflected when the press member <b>2</b> lies in a position other than the recessed portion (see <figref idref="DRAWINGS">FIG. 1</figref>); or

the sheet material P is deflected when the press member <b>2</b> lies in a position near the recessed portion <b>1</b><i>a </i>(see <figref idref="DRAWINGS">FIG. 2</figref>). For this purpose, a second memory (not shown) for storing the deformation amount of the elastic support member <b>3</b> when the sheet material P is not deflected, and a deformation amount difference calculating means (not shown) for calculating a difference between “the deformation amount of the elastic support member <b>3</b> when the sheet material P is deflected” and “the deformation amount stored in the second memory” may be provided to discriminate the kind of the sheet material from the difference in deformation amounts. In this case, a third memory (not shown) storing a relationship between the difference in deformation amount and the kind of the sheet material, and a second discrimination unit (not shown) for discriminating the kind of sheet material from the result by the deformation amount difference calculating means and data in the third memory may be provided to discriminate the kind of sheet material by the second discrimination unit.

Furthermore, in the apparatus shown in <figref idref="DRAWINGS">FIGS. 1 and 2</figref>, the press member <b>2</b> is moved, but this embodiment is not limited thereto, and the substrate and the recessed portion may be moved with the press member <b>2</b> fixed at a certain position. <figref idref="DRAWINGS">FIGS. 7 to 10</figref> show one example thereof, in which a roller <b>11</b> having a recessed portion <b>11</b><i>a </i>is rotated instead of moving press member <b>2</b>.

When the change of deformation amount of the elastic support member is detected in the process of change in deflection amount of the sheet material, and the kind of the sheet material is discriminated based on the change in deformation amount, a fourth memory (not shown) for storing as data a relationship between the deformation amount of the elastic support member <b>3</b> and the kind of sheet material, and a third discrimination unit (not shown) for discriminating the kind of the sheet material from the detected change in deformation amount of the elastic support member <b>3</b> and data in the fourth memory may be provided.

In addition, press force imparting means for imparting a press force to the press member <b>2</b> may be provided. Such press force imparting means may include:

means such that the press member holding means <b>4</b> is tilted to apply a bending moment to the press member <b>2</b> as shown by symbol D<b>1</b> in <figref idref="DRAWINGS">FIG. 1</figref>; and

a load is applied directly to the press member <b>2</b> as shown by symbol W in <figref idref="DRAWINGS">FIGS. 7 to 10</figref> instead of applying a bending moment. Furthermore, the load W may be a concentrated load or distributed load, and the load application point may be just above the press member <b>2</b> or at a different location.

The press member holding means <b>14</b> shown in <figref idref="DRAWINGS">FIGS. 3 to 6</figref> rotatably supports the press member <b>12</b> so that the press member <b>12</b> comes close to or moves away from the recessed portion <b>1</b><i>a</i>, wherein

the sheet material P is deflected when the press member <b>12</b> is close to the recessed portion <b>1</b><i>a</i>; and

the sheet material P is not deflected when the press member <b>12</b> is at a distance from the recessed portion <b>1</b><i>a</i>. Even in the case of an apparatus having such a configuration, press force imparting means for imparting a press force to the press member <b>12</b> may be provided. The press force imparting means may include a spring member installed between the press member <b>12</b> and the press member holding means <b>14</b> (see symbol <b>15</b>). A force F<b>1</b> acting on the sheet material P from the press member <b>12</b> equals a sum of a force F<b>2</b> acting on the press member <b>12</b> from the sheet material P and a force F<b>3</b> acting on the press member <b>12</b> from an elastic support member <b>13</b> (i.e. F<b>1</b>=F<b>2</b>+F<b>3</b>). Here, provided that the magnitude of F<b>1</b> is constant irrespective of the kind of the sheet material, the magnitudes of F<b>2</b> and F<b>3</b> depend on the material quality of the sheet material P such that the reaction force F<b>2</b> increases while the force F<b>3</b> decreases for a sheet material of high rigidity, and the reaction force F<b>2</b> decreases while the force F<b>3</b> increases for a sheet material of low rigidity. When the deformation amount of the elastic support member <b>13</b> is detected with the sensor S, the magnitude of F<b>3</b> can be known and as a result, the material quality of the sheet material P can be discriminated.

In the apparatus shown in <figref idref="DRAWINGS">FIGS. 1 and 2</figref>, the elastic support member <b>3</b> and the press member <b>2</b> are coupled together and placed outside the recessed portion <b>1</b><i>a</i>, and the elastic support member <b>3</b> is deformed when the press member <b>2</b> presses the sheet material P, but this embodiment is not limited to such a structure. For example, a structure is also acceptable in which the press member is placed outside the recessed portion <b>1</b><i>a </i>as shown by symbol <b>12</b> in <figref idref="DRAWINGS">FIGS. 3 to 6</figref>, the elastic support member is placed inside the recessed portion <b>1</b><i>a </i>as shown by symbol <b>13</b> in these figures, and the elastic support member <b>13</b> is deformed on the basis of pressing it via the sheet material P by the press member <b>12</b>.

In addition, elastic support members <b>3</b> and <b>13</b> in these figures are cantilever beams (flat springs) supported horizontally, but as long as they are elastically deformed, they may have shapes other than the plane shape, may be twin beams instead of cantilever beams, or may be supported vertically instead of being supported horizontally. Furthermore, if elastic support members <b>3</b> and <b>13</b> are flat springs, they may be made of stainless steel, carbon steel, Si—Mn steel, Cr—V steel, brass, beryllium copper and the like.

Here, the deformation amount sensor S may be a piezoelectric member, specifically a piezoelectric member made of lead zirconate titanate (PZT), barium titanate or zinc oxide.

It is sufficient that the recessed portion in the present invention can sustain deflection of a certain area of the sheet material P occurring when the press force is applied. Thus, the recessed portion conceptionally includes not only the substrate surface having only a certain area recessed (recessed area such as groove) as shown by symbols <b>1</b><i>a </i>and <b>11</b><i>a </i>in <figref idref="DRAWINGS">FIGS. 1 and 10</figref>, but also a portion cutting through the substrate from the front side to the back side such as a hole or opening.

In addition, the substrate in the present invention is not limited as long as it holds a part of sheet material P when the press force is applied, and conceptionally includes a plane plate-like platen (e.g. platen of image forming apparatus) as shown by symbol in <figref idref="DRAWINGS">FIGS. 1 to 6</figref>, a rotating roller (e.g. paper feed roller) as shown by symbol <b>11</b> in <figref idref="DRAWINGS">FIGS. 7 and 10</figref>, and other forms. That is, the substrate may be only capable of holding the sheet material P and sustaining the deflection of a certain area of the sheet material, and therefore it may be a ring, cylinder, rod or the like in shape.

Furthermore, the sheet material P may be a printing paper or the like.

The press member <b>2</b> shown in <figref idref="DRAWINGS">FIG. 1</figref> and the like is a roller rotatably supported by a rotating shaft, but may have a form other than the roller. For press members <b>2</b> and <b>12</b>, materials having large Young's modulus and hardness and specifically, they may be made of any of iron, nickel, chromium, tungsten, molybdenum, alloys thereof, oxides of these metals, aluminum oxides, silicon oxides, silicon nitrates, zircon oxides, ceramics thereof, glass and polymer materials.

The sheet-material discriminating apparatuses having various configurations described above may be provided in image forming apparatuses such as copiers and printers to detect the kind of a sheet material (i.e. printing paper).

A method for discriminating a sheet material according to the present invention will now be described.

The method for discriminating a sheet material according to the present invention comprises:

a step of deflecting a predetermined area of a sheet material by applying a press force F<b>1</b> thereto;

a step of placing an elastic support member so that the elastic support member is deformed by an amount corresponding to a deflection amount of the sheet material;

a step of detecting a deformation amount of the elastic support member; and

a step of discriminating the kind of a sheet material based on the results of the detection.

Advantages of this embodiment will now be described.

According to this embodiment, the kind of a sheet material P is discriminated while the sheet material P is supported by a substrate <b>1</b>. Thus, the sheet material P is hard to be deflected by its weight even when it is thin (or it has a low bending rigidity), the sheet material is hard to be displaced under influences of wind and mechanical vibrations, and the amount of deflection of the sheet material P by press members <b>2</b> and <b>12</b> can be accurately detected to correctly discriminate the kind of the sheet material P.

In addition, according to this embodiment, the sheet material P is hard to be displaced under influences of wind and mechanical vibrations, thus making it possible to correctly discriminate the kind of sheet material P in the process of feeding of the sheet material P.

Furthermore, when a piezoelectric member is used as a deformation amount sensor S, no power source is required for detecting a signal of deformation, thereby resulting in a simplified structure.

Furthermore, the above recessed portion preferably has a depth sufficient to prevent the sheet material from contacting the bottom of the recessed portion even when the sheet material is pressed with the press member.

The present invention will be described further in detail below based on Examples.

Example 1

In this Example, an apparatus A<b>1</b> shown in <figref idref="DRAWINGS">FIGS. 1 and 2</figref> was fabricated.

<figref idref="DRAWINGS">FIGS. 1 and 2</figref> well represent the feature of the present invention and in these figures, reference numeral <b>1</b> denotes a platen on which a printing paper (sheet material) P is placed, and reference symbol <b>1</b><i>a </i>denotes a groove (recessed portion) formed in the platen <b>1</b>. In addition, reference numeral <b>3</b> denotes a flat spring (elastic support member), reference symbol S denotes a piezoelectric member (deformation amount sensor) provided on the surface of the flat spring <b>3</b>, reference numeral <b>5</b> denotes a press shaft integrated with the flat spring <b>3</b>, reference numeral <b>2</b> is a roller (press member) for pressing the printing paper P, and reference numeral <b>4</b> denotes a movable fixed end (press member holding means) for supporting the flat spring <b>3</b> and the roller <b>2</b> and moving them along the printing paper P.

Then, in the configuration described above, the printing paper P is placed on the platen <b>1</b>, the roller <b>2</b> is placed above the printing paper P and at a position other than the groove <b>1</b><i>a </i>and thereafter, the movable fixed end <b>4</b> is rotated in the direction of arrow D<b>1</b> as shown in <figref idref="DRAWINGS">FIG. 1</figref>. Consequently, the roller <b>2</b> contacts the printing paper P, and thus the flat spring <b>3</b> is deflected. As the movable fixed end <b>4</b> is moved in the direction of arrow D<b>2</b>, the roller <b>2</b> causes the printing paper P to be deflected towards the groove <b>1</b><i>a </i>as shown in <figref idref="DRAWINGS">FIG. 2</figref>. Furthermore, when the movable fixed end <b>4</b> is rotated in the direction of arrow D<b>1</b> (i.e. the roller <b>2</b> contacts the printing paper P), a bending moment occurs in the flat spring <b>3</b>, and the bending moment changes in the following manner as the roller <b>2</b> moves in the direction of arrow D<b>2</b>. Specifically, the bending moment

is kept constant when the roller <b>2</b> lies in a position other than the groove <b>1</b><i>a</i>, but

gradually decreases when the roller <b>2</b> enters the groove <b>1</b><i>a, </i>

decreases to a minimum when the roller <b>2</b> reaches almost the center of the groove a<b>1</b> (a position at which deflection of its printing paper P reaches a maximum) (see <figref idref="DRAWINGS">FIG. 2</figref>),

gradually increases as the roller <b>2</b> moves from the center of the groove <b>1</b><i>a </i>to the periphery, and

becomes constant when the roller <b>2</b> leaves the groove <b>1</b><i>a. </i>

Furthermore, the deformation amount of the flat spring <b>3</b> changes in proportion to the magnitude of the bending moment, and the deformation amount is detected with the piezoelectric member S (in the strict sense, the piezoelectric member S is deformed, and the deformation amount thereof is detected as a voltage value). The output voltage of the piezoelectric member S varies depending on the kind of the printing paper P (bending rigidity in the strict sense) (specifically, the output voltage decreases when the bending rigidity increases, and the output voltage increases when the bending rigidity decreases), and the kind of printing paper P can be discriminated from the output voltage.

Ordinary paper (CP 250 manufactured by Canon Inc.), coat paper (HR 101s manufactured by Canon Inc.) and glossy paper (PR 101 manufactured by Canon Inc.) were set one after another to determine the output voltage of the piezoelectric member S and as a result, it was found that the output voltage of the ordinary paper was the highest value, and the output voltages of the coat paper and the glossy paper decreased in mentioned order.

According to this Example, the kind of a printing paper P is discriminated in a state that the printing paper P placed on the platen <b>1</b>, and therefore the kind can be correctly discriminated even when the printing paper P is thin, and wind and mechanical vibrations occur.

Furthermore, the discrimination of a paper in this Example is performed using the output voltage of the piezoelectric member S when the printing paper is most deflected, but the discrimination of a paper may be performed using a difference between the output voltage when the printing paper is not deflected and the output voltage when the printing paper is most deflected, or using a rate of change in output voltage in the process of deflection of the printing paper.

Example 2

In this Example, an apparatus A<b>3</b> shown in <figref idref="DRAWINGS">FIGS. 7 to 10</figref> was fabricated. Furthermore, the same parts as those of Example 1 are given the same symbols, and overlapped descriptions thereof are omitted here.

<figref idref="DRAWINGS">FIGS. 7 to 10</figref> well represent the feature of the present invention and in these figures, reference numeral <b>10</b> denotes a platen on which a printing paper P is placed, reference symbol <b>10</b><i>a </i>denotes a cylindrical hollow portion formed on the platen <b>10</b>, reference numeral <b>11</b> denotes a lower roller (corresponding to the “substrate” described in claims) installed in the hollow portion <b>10</b><i>a</i>, and reference symbol <b>11</b><i>a </i>denotes a recessed portion formed in the lower roller <b>11</b>. In addition, reference numeral <b>4</b> denotes a movable fixed end (press member holding means) supporting a flat spring <b>3</b> and an upper roller <b>2</b> and moving them along the printing paper P. Furthermore, this movable fixed end <b>4</b> cannot be rotated unlike the movable fixed end of Example 1, but the upper roller <b>2</b> is pressed against the printing paper P by applying a concentrated load W along the axis of a press shaft <b>5</b>.

Then, in the configuration described above, the printing paper P is placed on the platen <b>10</b> as shown in <figref idref="DRAWINGS">FIG. 7</figref>, and the upper roller <b>2</b> is placed on the printing paper P to apply the load W.

As the lower roller <b>11</b> is rotated in this state, the deflection amount of the flat spring <b>3</b> changes in the following manner. Specifically, the deflection amount of the flat spring <b>3</b>

remains unchanged when the recessed portion <b>11</b><i>a </i>lies at a position other than the position of the upper roller <b>2</b>, but

gradually increases while the recessed portion <b>11</b><i>a </i>rotates and the upper roller <b>2</b> enters the recessed portion <b>11</b><i>a, </i>

reaches the maximum at the time when the center of the recessed portion <b>11</b><i>a </i>matches the upper roller <b>2</b> (see <figref idref="DRAWINGS">FIGS. 9 and 10</figref>),

gradually decreases as the recessed portion <b>11</b><i>a </i>further rotates, and

becomes constant when the roller <b>2</b> leaves the recessed portion <b>11</b><i>a. </i>

Furthermore, the deformation amount of the flat spring <b>3</b> is detected with the piezoelectric member S, and by determining a change in strain amount per unit time (dε/dt), the kind of paper can be discriminated.

Ordinary paper (New Printer Paper; CP 250 manufactured by Canon Inc.), coat paper (Ultra Glossy Thick type; PR 101 manufactured by Canon Inc), OHP paper (Color BJ Transparency; CF 301 manufactured by Canon Inc) were set one after another to determine the strain amounts thereof. As a result, it was found that the strain amount of ordinary paper, glossy paper and OHP paper decreased in mentioned order, i.e. ordinary paper&gt;glossy paper&gt;OHP paper. Thus, in this Example, the same effect as that of Example 1 could be obtained.

Furthermore, the piezoelectric member S was bonded to the flat spring <b>3</b> with an adhesive, and no voltage was applied to the piezoelectric member S.

When this method is used, no input power source to the piezoelectric member S is required, and therefore electric circuitry for measurement is simplified, and power savings are achieved. Because the hollow portion <b>10</b><i>a </i>is provided in the platen <b>10</b> on which the printing paper P is placed, and the kind of paper is detected in the process of transference of the printing paper P over the hollow portion <b>10</b><i>a </i>from a paper feeding tray, the structure is simplified.

Furthermore, in this Example, the load W is a fixed load, and always presses the printing paper P, and when the upper roller <b>2</b> lies in the recessed portion <b>11</b><i>a </i>in association with rotation of the lower roller <b>11</b>, the printing paper P is deflected and at the same time, the flat spring <b>3</b> is deformed in response to the deflection.

In this Example, the recessed portion <b>11</b><i>a </i>had a depth of 1 mm, a width of 3 mm and a length of 5 mm, the roller <b>11</b> had a diameter of 10 mm, and the load W was any fixed load in the range of 10 gf to 50 gf, which was provided by a coil spring (not shown). Beryllium copper was used as the flat spring <b>3</b>, and lead zirconate titanate was used as the piezoelectric member S.

According to this Example, the structure is simplified, and power savings are achieved because no input power source for measuring sensors is required. In addition, because the kind of paper is detected during a dynamic period over which the printing paper P is transferred from the paper feeding tray to a print location, it is not necessary to temporarily stop the feeding of paper for detection of the kind of paper, thus making it possible to save time.

Example 3

In this Example, an apparatus A<b>2</b> shown in <figref idref="DRAWINGS">FIGS. 3 to 6</figref> was fabricated. Furthermore, the same parts as those of Examples 1 and 2 are given the same symbols, and overlapped descriptions thereof are omitted here.

<figref idref="DRAWINGS">FIGS. 3</figref>, <b>4</b>, <b>5</b> and <b>6</b> well represent the feature of the present invention, and a roller <b>14</b> for feeding a printing paper was placed above a recessed portion <b>1</b><i>a </i>of a platen <b>1</b>. A hole portion <b>14</b><i>a </i>was provided in the roller <b>14</b>, and a coil spring <b>15</b> and a press member <b>12</b> were placed in the hole portion <b>14</b><i>a</i>. That is, the roller <b>14</b> serves as press member holding means, and the coil spring <b>15</b> serves as press force imparting means for imparting a press force to the press member <b>12</b>. In addition, a flat spring (elastic support member) <b>13</b> supported on one side and a piezoelectric member (deformation amount sensor) S bonded to the flat spring <b>13</b> were placed in the recessed portion <b>1</b><i>a </i>of the platen <b>1</b>. Furthermore, reference symbol <b>13</b><i>a </i>denotes a raised portion situated at the leading end of the flat spring <b>13</b> and contacting the printing paper P.

The apparatus A<b>2</b> fabricated in this Example has a configuration such that the printing paper P is held between the platen <b>1</b> and the roller <b>14</b> because the roller <b>14</b> has an axial length greater than the size of the recessed portion <b>1</b><i>a </i>as shown in <figref idref="DRAWINGS">FIG. 4</figref>. Thus, when this roller <b>14</b> is rotated, the printing paper P is fed over the platen. Here, the printing paper P is never deflected in the recessed portion <b>1</b><i>a </i>as long as the press member <b>12</b> does not enter the recessed portion <b>1</b><i>a</i>, but the printing paper P is deflected inwardly in the recessed portion <b>1</b><i>a </i>when the roller <b>14</b> rotates to cause the press member <b>12</b> to enter the recessed portion <b>1</b><i>a </i>(see <figref idref="DRAWINGS">FIGS. 5 and 6</figref>), and the flat spring <b>13</b> is deformed. Furthermore, the deformation amount gradually increases as the roller <b>14</b> rotates, reaches a maximum in the state of <figref idref="DRAWINGS">FIG. 5</figref>, and then decreases. Accordingly, the strain amount of the piezoelectric member S changes, which is detected as a change in voltage.

In this Example, the recessed portion <b>1</b><i>a </i>had a depth of 2 mm, a width of 5 mm and a length of 20 mm, and the roller <b>14</b> had a diameter of 10 mm. In addition, the spring force of the coil spring <b>15</b> described above could be adjusted with a screw (not shown), and a press force from the press member <b>12</b> could be arbitrarily set within the range of 10 gf to 50 gf. Furthermore, the flat spring <b>13</b> and the raised portion <b>13</b><i>a </i>were adjusted so that the raised portion <b>13</b><i>a </i>always contacted the printing paper P.

Ordinary paper (New Printer Paper; CP 250 manufactured by Canon Inc.), glossy paper (Ultra Glossy Thick type; PR 101 manufactured by Canon Inc), OHP paper (Color BJ Transparency; CF 301 manufactured by Canon Inc) were set one after another with the press force kept contact to determine the voltage of the piezoelectric member S and as a result, it was found that the voltage value decreases in order of ordinary paper, glossy paper and OHP paper, i.e. ordinary paper&gt;glossy paper&gt;OHP paper. Thus, this can be used to discriminate the kind of paper.

Furthermore, in this Example, stainless steel (SUS 27) was used for the press member <b>12</b>, but any material having a high Young's modulus, a high hardness and a wide elastic range may be used and for example, iron, nickel, chromium, tungsten and molybdenum are preferable, or alloys or oxides thereof, or aluminum oxides, silicon oxides, silicon nitrates and zircon oxides, or ceramics thereof, or glass or polymer materials may be used.

Furthermore, in this Example, phosphorous bronze was used for the flat spring <b>13</b> but instead thereof, for example, carbon steel, Si—Mn steel, Cr—V steel, brass and beryllium copper may be used. Furthermore, PZT (lead zirconate titanate) was used for the piezoelectric member S but instead thereof, for example, barium titanate, ZnO, and any material having a piezoelectric property may be used.